Highly efficient microbial inactivation enabled by tunneling charges injected through two-dimensional electronics

Airborne pathogens retain prolonged infectious activity once attached to the indoor environment, posing a pervasive threat to public health. Conventional air filters suffer from ineffective inactivation of the physics-separated microorganisms, and the chemical-based antimicrobial materials face challenges of poor stability/efficiency and inefficient viral inactivation. We, therefore, developed a rapid, reliable antimicrobial method against the attached indoor bacteria/viruses using a large-scale tunneling charge–motivated disinfection device fabricated by directly dispersing monolayer graphene on insulators. Free charges can be stably immobilized under the monolayer graphene through the tunneling effect. The stored charges can motivate continuous electron loss of attached microorganisms for accelerated disinfection, overcoming the diffusion limitation of chemical disinfectants. Complete (>99.99%) and broad-spectrum disinfection was achieved <1 min of attachment to the scaled-up device (25 square centimeters), reliably for 72 hours at high temperature (60°C) and humidity (90%). This method can be readily applied to high-touch surfaces in indoor environments for pathogen control.


Fig. S1.
Schematics showing the structure of the TCD device.(A) The graphene monolayer covers the entire SiO2 surface charge, and tunneling charges can be injected through the graphene monolayer and stored on the SiO2 surface.The TCD device enables disinfection once microorganisms are attached.(B) Measurement of microbial surface charges in the bioaerosol, indicating that the opposite surface charges between microorganisms (negative) and the surface of the TCD device (positive) can promote the attachment of microorganisms.The potential of the deionized water before and after the collection of the microbial aerosol was measured using a Faraday cup and a multimeter (Keysight, 34470A).

Fig. S2.
Schematics showing the structure of the AFM-based micro-transistor enabling tunneling charge storage.An AFM tip with a 10 V bias was brought into contact with and scanned across the graphene monolayer on the SiO2 insulator within an area of 4 µm × 4 µm with a force of 20 nN.Charges from the AFM tip were injected across the graphene monolayer, followed by trapping the charges on the SiO2 surface.Adhesion energy (i.e., binding force) between the graphene monolayer and SiO2 using DFT simulation.The DFT simulation was performed using Materials Studio (2020, BIOVIA).The Broyden-Fletcher-Goldfarb-Shanno algorithm with the Perdew-Burke-Ernzerhof exchangecorrelation function under the generalized gradient approximation was used to optimize the structure.The DFT models consisting of graphene monolayer and SiO2 were investigated using a plane-wave basis with cutoff energies of 680 and 750 eV, respectively.A standard normconserving pseudopotential was used to describe the electron-ion interaction.To avoid spurious interactions between neighboring unit cells in contact and slab models, a vacuum region spanning more than 15 Å was created.

Fig. S20.
Quality control of the extracted RNA.The optical density (OD) of the extracted RNA was measured at 230, 260, and 280 nm.The OD260/280 and OD260/230 indices were higher than 1.9, indicating the high quality of the extracted RNA with complete structure and high purity.The quality of the extracted RNA was also examined using a bioanalyzer.The extracted intracellular RNA showed a high RNA integrity number (RIN) of 9.5 after the attachment of the bacteria to the TCD device.Therefore, the extracted RNA showed high quality in terms of structural integrity, and we confirmed that the charge transfer process was ineffective for RNA damage.

Fig. S3 .
Fig. S3.Fabrication of graphene monolayers.(A) Illustration of the CVD system for the fabrication of graphene monolayers.(B) Operating conditions of the CVD process for fabricating graphene monolayers.(C) SEM image of the fabricated graphene monolayers on the Cu foil.(D) Raman spectra of the graphene monolayer, showing the peak of G and 2D at ~1600 and ~2700 cm -1 .The ratios of    2 = 0.5 indicate the as-prepared graphene as a monolayer structure.

Fig. S4 .
Fig. S4.Schematic illustration of the air gap thickness of the TCD device.Considering the measured vertical height of graphene on the SiO2 substrate (1.0 nm) and the theoretical thickness of the graphene monolayer (0.3 nm), the air gap thickness can be estimated to be around 0.7 nm.(A) Schematic of the air gap thickness.(B) Topography image of as-prepared graphene on SiO2.(C) Linear scan showing the cross-sectional profile along the dashed lines in B.

Fig. S5 .
Fig. S5.Confirmation of charge tunneling.Experiments were performed by comparing the potential difference (ΔV) with and without a graphene monolayer and with a conductive Cu substrate replacing the SiO2 insulator.Besides the TCD device consisting of graphene monolayers covering the SiO2, control experiments with graphene monolayers covering a conductive substrate (Cu plate) and bare SiO2 were set up.Only the TCD device allows charge tunneling and immobilization.Error bars represent the standard deviation (n = 3).Significant differences among groups are indicated by * and ** for p < 0.05 and < 0.01, respectively.

Fig. S6 .
Fig. S6.Effect of HOPG on charge injection.HOPG was fabricated by the exfoliation process without defects, while the CVD-fabricated graphene had multiple defects.When HOPG is used instead of the CVD-fabricated graphene, few charges can be injected.

Fig. S7 .
Fig. S7.Effect of humidity and temperature on charge retention after 72 h.Humidity was controlled from 10 to 90% and temperature was controlled from 15 to 60 °C.

Fig. S8 .
Fig. S8.Photos of a scaled-up TCD device.The device was fabricated by dispersing graphene monolayers with a controlled area of 5 cm × 5 cm on a SiO2-coated Si wafer.

Fig. S9 .
Fig. S9.Schematic illustration of charge injection for a scaled-up TCD device.The device consisted of a graphene monolayer covering the SiO2 surface (5 cm  5 cm), an external power supply, a Cu foil with a bias voltage (10 V), and a 1 kg weight (corresponding to an external pressure of 4000 Pa).

Fig. S10 .
Fig. S10.Effect of charging voltage (1 − 20 V) on the surface potential of TCD device.The experiment was performed at a fixed temperature (20 °C) and humidity (30%).

Fig. S11 .
Fig. S11.Effect of the charging voltage on the viral inactivation efficiency.Dashed lines indicate that all viruses (MS2) tested were inactivated (i.e., no live MS2 was detected).Error bars represent the standard deviation (n = 3).Significant differences among groups are indicated by * and ** for p < 0.05 and < 0.01, respectively.

Fig. S12 .
Fig. S12.Effect of the finger touch on the charge distribution and microbial inactivation efficiency.(A and B) Distribution of potential (ΔV) from charge tunneling on the device surface before (A) and after (B) finger touch.(C) Microbial inactivation efficiency of the device before and after finger touch.Dashed lines indicate that all microorganisms tested were inactivated (i.e., no live microorganisms were detected).Error bars represent the standard deviation (n = 3).Significant differences among groups are indicated by * and ** for p < 0.05 and < 0.01, respectively.

Fig
Fig. S13.Adhesion energy (i.e., binding force) between the graphene monolayer and SiO2 using DFT simulation.The DFT simulation was performed using Materials Studio (2020, BIOVIA).The Broyden-Fletcher-Goldfarb-Shanno algorithm with the Perdew-Burke-Ernzerhof exchangecorrelation function under the generalized gradient approximation was used to optimize the structure.The DFT models consisting of graphene monolayer and SiO2 were investigated using a plane-wave basis with cutoff energies of 680 and 750 eV, respectively.A standard normconserving pseudopotential was used to describe the electron-ion interaction.To avoid spurious interactions between neighboring unit cells in contact and slab models, a vacuum region spanning more than 15 Å was created.

Fig. S14 .
Fig. S14.Effect of humidity (up to 90%) and temperature (up to 60 °C) on the efficacy of the TCD device for B. subtilis and MS2 inactivation after 48 and 72 h.The TCD device was charged at 10 V, and microorganisms were measured after 1 min of attachment.Dashed lines indicate that all microorganisms were inactivated (i.e., no live microorganisms were detected).

Fig. S15 .
Fig. S15.Effect of the high temperature (60 °C) or high humidity (90%) on microbial survival.No charging voltage was applied to the TCD device, and microorganisms were measured after attachment for 1.0, 2.0, and 5.0 min.Error bars represent standard deviation (n = 3).

Fig. S16 .
Fig. S16.Effect of the TCD device for viral inactivation when treating intermittently applied aerosols containing MS2.The experiment was performed at a fixed temperature (20 °C) and humidity (30%).The TCD device was charged at 10 V, and microorganisms were measured after 1 min of attachment.Dashed lines indicate that all viruses (MS2) were inactivated (i.e., no live MS2 was detected).

Fig. S17 .
Fig. S17.Intracellular generation of ROS in bacteria after attachment to the TCD at charging voltages of V and 20 V. (A) ROS in bacteria when the TCD was charged for 0.5 h.(B) ROS in bacteria when the TCD was charged for 72 h.Microorganisms were evaluated after 1 min of attachment.The experiment was performed at a fixed temperature (20 °C) and humidity (30%).Error bars represent standard deviation (n = 3).Significant differences among groups are indicated by * and ** for p < 0.05 and < 0.01, respectively.

Fig. S18 .
Fig. S18.The activity of the bacterial SOD enzyme after attachment to the TCD at charging voltages of 10 V and 20 V. (A) SOD activity in bacteria when the TCD was charged for 0.5 h.(B) SOD activity in bacteria when the TCD was charged for 72 h.Microorganisms were evaluated after 1 min of attachment.The experiment was performed at a fixed temperature (20 °C) and humidity (30%).Error bars represent standard deviation (n = 3).Significant differences among groups are indicated by * and ** for p < 0.05 and < 0.01, respectively.

Fig. S19 .
Fig. S19.The activity of the bacterial antioxidant enzyme after attachment to the TCD at charging voltages of 10 V and 20 V. (A) Antioxidant enzyme activity in bacteria when the TCD was charged for 0.5 h.(B) Antioxidant enzyme activity in bacteria when the TCD was charged for 72 h.Microorganisms were evaluated after 1 min of attachment.The experiment was performed at a fixed temperature (20 °C) and humidity (30%).Error bars represent standard deviation (n = 3).Significant differences among groups are indicated by * and ** for p < 0.05 and < 0.01, respectively.